1. Field of the Invention
The present invention relates to a video signal reproducing apparatus comprising a display means for displaying a reproduced video signal, and a video signal display apparatus, and more particularly to such apparatus suitable for displaying a video image on a liquid crystal display means.
2. Description of the Related Art
A helical scan type video signal reproducing apparatus generally reproduces a signal with at least two magnetic heads (hereinafter referred to as xe2x80x9cCH1 headxe2x80x9d and xe2x80x9cCH2 headxe2x80x9d) mounted on a rotary drum and having different azimuth angles. A magnetic tape has oblique tracks on which a video signal is recorded. The oblique tracks are alternately formed by the respective magnetic heads at azimuth angles equal to those of the corresponding magnetic heads. When this magnetic tape is driven for reproduction at a velocity n times (n is an integer) higher than a recording speed, each of the magnetic heads reproduces a signal while traversing (nxe2x88x921) tracks (at an equal velocity (n=1), the magnetic head does not traverse any tracks since the magnetic head scans the tape at an oblique angle equal to an oblique angle of the tracks when they were recorded). Thus, an even number of tracks are traversed by the magnetic head when n is an odd number, while an odd number of tracks are traversed when n is an even number (including n=0).
On the other hand, each of the magnetic heads outputs a reproduced signal only when it scans a track which has the same azimuth angle, and outputs a noise signal when it scans a track which has a different azimuth angle. Therefore, when reproduction is performed, for example, at a velocity four times higher (n=4), the magnetic heads each traverse three tracks. In this event, if a CH1 head reproduces in order a track with the same azimuth angle, a track with a different azimuth angle, and a track with the same azimuth angle, a CH2 head reproduces in order a track with the different azimuth angle, a track with the same azimuth angle, and a track with the different azimuth angle. Stated another way, when reproduction is performed at a velocity even-number times higher, the CH1 head and the CH2 head reproduce signals whose envelope is in an opposite phase relationship (complementary).
When video signals reproduced by the above-mentioned magnetic heads are displayed on a display means having a memory effect, such as a liquid crystal display device, the display operation utilizes the opposite phase relationship between reproduced signals of the respective magnetic heads. By writing outputs of the CH1 head and the CH2 head into the display means only during a period in which effective reproduced signals are being outputted, a favorable noise-free search image or still image (when n=0) can be reproduced over the entire screen.
The prior art related to a video signal reproducing apparatus for providing such a favorable noise-free trick reproduced signal is disclosed, for example, in JP-A-8-65636 and JP-A-9-106502 which describe a video signal processing apparatus.
It is an object of the present invention to provide a display apparatus, and a reproducing apparatus comprising the same, which prevent a displayed video image from changing into a brighter or darker image, so that the user will not have a feeling of strangeness in the progress of the displayed video image, even if a video signal is discontinuously written into a liquid crystal display means or any other video display means which has a memory effect.
More specifically, when a video signal is discontinuously written into the liquid crystal display means as mentioned above, the amount of polarization of liquid crystal is gradually attenuated during a period in which the video signal is not written. For this reason, with a liquid crystal display means having a back light function, light from a back light source more easily transmits the liquid crystal. Likewise, with a liquid crystal display means having a reflector, reflected light more easily transmits the liquid crystal. In other words, this means that a displayed video image changes in a brighter direction. Thus, as compared with normal reproduction (when n=1) where a video signal is continuously written into the liquid crystal display means, a displayed video image becomes brighter when trick reproduction (n is an even integer) is performed to discontinuously write a video signal into the liquid crystal display means, resulting in giving the user a feeling of strangeness.
This phenomenon constitutes a problem which arises not only in the liquid crystal display means but also similarly in a video display means which displays a video image while accumulating the level of the video signal in analog amount. In the latter case, a displayed video image may change in a brighter or darker direction depending on the characteristics of a particular video display means.
To solve the problem mentioned above, the present invention has taken the following measures.
A video signal reproducing apparatus according to the present invention is a helical scan type video signal reproducing apparatus for reproducing a video signal from a magnetic tape wrapped around a rotary drum having magnetic heads mounted thereon. The apparatus comprises a tape driving controller for controlling driving of the magnetic tape, a reproduced signal processing circuit for processing output signals from the magnetic heads to generate a reproduced video signal, a liquid crystal display circuit for displaying the reproduced video signal, a write controller for writing the reproduced video signal into the liquid crystal display circuit, and a brightness controller for controlling the brightness for the liquid crystal display circuit. The brightness controller controls the liquid crystal display circuit to display a brighter image thereon when the write controller continuously writes the reproduced video signal into the liquid crystal display circuit, while the brightness controller controls the liquid crystal display circuit to display a darker image thereon when the write controller discontinuously writes the reproduced video signal into the liquid crystal display circuit.
With the configuration set forth above, it is possible to control the brightness for the liquid crystal display circuit at the same level both when a video signal is continuously written into the liquid crystal display circuit and when a video signal is discontinuously written into the liquid crystal display circuit, thereby suppressing a feeling of visual strangeness.
Specifically, the write controller discontinuously writes a reproduced video signal into the liquid crystal display circuit when the magnetic heads each scan the oblique tracks on the magnetic tape at an oblique angle different from the oblique angles of the oblique tracks, and the tape driving controller controls driving of the magnetic tape such that envelope of signals reproduced from the plurality of magnetic heads is in an alternately opposite phase relationship. The write controller writes the reproduced video signal into the liquid crystal display circuit during a period in which the magnetic heads reproduce tracks with the same azimuth angles, and the write controller controls to stop writing the reproduced video signal into the liquid crystal display circuit during a period in which the magnetic heads reproduce tracks with different azimuth angles.
The video signal reproducing apparatus according to the present invention further comprises a reference brightness register for supplying the brightness controller with reference brightness. Specifically, the brightness controller controls the brightness for the liquid crystal display circuit based on the reference brightness when the write controller continuously writes a reproduced video signal into the liquid crystal display circuit, and the brightness controller controls the liquid crystal display circuit to display an image of brightness lower than the reference brightness when the write controller discontinuously writes a reproduced video signal into the liquid crystal display circuit. In addition, an input terminal is provided for the user to set the reference brightness supplied by the reference brightness register.
Thus, the brightness of a displayed video image is controlled at brightness set by the user himself in either of a mode in which a video signal is continuously written and a mode in which a video signal is discontinuously written, thereby making it possible to provide the user with more consistent images on the liquid crystal display circuit.
Specifically, the brightness controller may be an amplitude controller for controlling the amplitude of a video signal written into a liquid crystal matrix circuit (brightness controller) or a controller for controlling the center of control in the liquid crystal matrix circuit of a video signal written into the liquid crystal matrix circuit (contrast controller).
Another video signal reproducing apparatus according to the present invention is a helical scan type video signal reproducing apparatus which comprises a tape driving controller, a reproduced signal processing circuit, a liquid crystal display circuit, and a brightness controller for controlling the brightness for the liquid crystal display circuit. The brightness controller controls the liquid crystal display circuit to display a darker image thereon when the tape driving controller controls the magnetic tape to run at a velocity even-number times (the even-number may be zero) as high as a velocity at which a video signal was recorded on the magnetic tape. On the other hand, the brightness controller controls the liquid crystal display circuit to display a brighter image thereon when the tape driving controller controls the magnetic tape to run at a velocity odd-number times as high as a velocity at which a video signal was recorded on the magnetic tape. With this configuration, the brightness of a displayed image can also be controlled appropriately in a manner similar to the aforementioned video signal reproducing apparatus.
In another aspect, a video display apparatus according to the present invention comprises a liquid crystal display circuit, a write controller, and a brightness controller for controlling the brightness for the liquid crystal display circuit. The brightness controller controls the liquid crystal display circuit to display a brighter image thereon when the write controller continuously writes a video signal into the liquid crystal display circuit, and the brightness controller controls the liquid crystal display circuit to display a darker image thereon when the write controller discontinuously writes a video signal into the liquid crystal display circuit.
Another video display apparatus according to the present invention comprises a display device, having a memory effect, for displaying a video signal, a write controller, and a brightness controller for controlling the brightness for the display device. When the display device has a characteristic of displaying a brighter video image as a write period is longer, the brightness controller controls the display device to display a brighter video image thereon when the write controller continuously writes a reproduced video signal into the display device, and the brightness controller controls the display device to display a darker video image thereon when the write controller discontinuously writes a reproduced video signal into the display device. On the other hand, when the display device has a characteristic of displaying a darker video image as the write period is longer, the brightness controller controls the display device to display a darker image thereon when the write controller continuously writes a reproduced video signal into the display device, and the brightness controller controls the display device to display a brighter image thereon when the write controller discontinuously writes a reproduced video signal into the display device.